Lee Seungku, Mortazawi Amir
IEEE Trans Ultrason Ferroelectr Freq Control. 2016 Mar;63(3):456-62. doi: 10.1109/TUFFC.2016.2517643.
This paper presents a ladder-type bulk acoustic wave (BAW) intrinsically switchable filter based on ferroelectric thin-film bulk acoustic resonators (FBARs). The switchable filter can be turned on and off by the application of an external bias voltage due to the electrostrictive effect in thin-film ferroelectrics. In this paper, Barium Strontium Titanate (BST) is used as the ferroelectric material. A systematic design approach for switchable ladder-type ferroelectric filters is provided based on required filter specifications. A switchable filter is implemented in the form of a BST-on-Si composite structure to control the effective electromechanical coupling coefficient of FBARs. As an experimental verification, a 2.5-stage intrinsically switchable BST-on-Si composite FBAR filter is designed, fabricated, and measured. Measurement results for a typical BST-on-Si composite FBAR show a resonator mechanical quality factor (Q(m)) of 971, as well as a (Q(m)) × f of 2423 GHz. The filter presented here provides a measured insertion loss of 7.8 dB, out-of-band rejection of 26 dB, and fractional bandwidth of 0.33% at 2.5827 GHz when the filter is in the on state at a dc bias of 40 V. In its off state, the filter exhibits an isolation of 31 dB.
本文提出了一种基于铁电薄膜体声波谐振器（FBAR）的梯型体声波（BAW）本征可切换滤波器。由于薄膜铁电体中的电致伸缩效应，该可切换滤波器可通过施加外部偏置电压来开启和关闭。本文中，钛酸锶钡（BST）被用作铁电材料。基于所需的滤波器规格，提供了一种可切换梯型铁电滤波器的系统设计方法。以BST - on - Si复合结构的形式实现了一种可切换滤波器，以控制FBAR的有效机电耦合系数。作为实验验证，设计、制作并测量了一个2.5级本征可切换的BST - on - Si复合FBAR滤波器。典型BST - on - Si复合FBAR的测量结果显示，谐振器的机械品质因数（Q(m)）为971，以及（Q(m)）×f为2423 GHz。当滤波器在40 V直流偏置下处于开启状态时，此处展示的滤波器在2.5827 GHz处的测量插入损耗为7.8 dB，带外抑制为26 dB，分数带宽为0.33%。在其关闭状态下，该滤波器表现出31 dB的隔离度。
